Splenic requirement for antigenic variation and expression of the variant antigen on the erythrocyte membrane in cloned Plasmodium knowlesi malaria.
AUTOR(ES)
Barnwell, J W
RESUMO
Variant antigens appear on the surface of Plasmodium knowlesi-infected erythrocytes as the asexual parasite matures and are detected by antibody-mediated schizont-infected cell agglutination (SICA). We now show that cloned parasites can undergo antigenic variation in nonsplenectomized monkeys. In addition, we previously described a new P. knowlesi phenotype in which uncloned parasites passaged in splenectomized monkeys were no longer agglutinable by immune sera. We have designated this new phenotype SICA[-] and the one expressing the variant antigen SICA[+]. Cloned parasites can also switch from SICA[+] to SICA[-] in splenectomized monkeys. The switch from SICA[+] to SICA[-] is a gradual process that requires sequential subpassage in several monkeys. After passage in one monkey, the agglutination titer decreased 4- to 16-fold. Decreased agglutination was associated with decreased antibody binding on all infected erythrocytes as measured by fluorescein-conjugated anti-rhesus monkey immunoglobulin. The asexual malaria parasite can therefore alter its expression of variant antigen in response to the host environment (antivariant antibody or splenectomy). When cloned SICA[-] parasites were inoculated into intact monkeys, two courses of parasitemia were observed: fulminant parasitemia (greater than 20%) and parasitemia that was controlled. Fulminant infections were associated with conversion of the parasite from SICA[-] to SICA[+], i.e., from nonexpression to expression of the variant antigen on the erythrocyte surface. Parasitized erythrocytes remained SICA[-] in those infections that were controlled. It appears, therefore, that the expression of the variant antigen on the erythrocyte surface may influence parasite virulence.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=348148Documentos Relacionados
- Antigenic variation of Plasmodium knowlesi malaria: identification of the variant antigen on infected erythrocytes.
- Humoral and cell-mediated immunity to the Plasmodium falciparum ring-infected erythrocyte surface antigen in an adult population exposed to highly endemic malaria.
- Expression of senescent antigen on erythrocytes infected with a knobby variant of the human malaria parasite Plasmodium falciparum.
- Altered expression of human monocyte Fc receptors in Plasmodium falciparum malaria.
- Reassessment of the role of splenic leukocyte oxidative activity and macrophage activation in expression of immunity to malaria.